This invention relates generally to marine engines and, more specifically, to cooling engine components during engine operation.
Marine engines typically include a cooling system for cooling at least portions of the engine exhaust system and the engine cylinders. For example, and in a known V-type marine engine, cooling water is supplied into a space between the cylinder banks, sometimes referred to herein as the engine valley. Water flows from the valley and to each cylinder bank. Specifically, a flow path is provided from the valley to each cylinder bank. The flow path to each cylinder bank does not, however, typically result in water flowing over the exhaust port of each cylinder, and water is not supplied directly to each cylinder from the valley. As a result, the hottest part of each cylinder (i.e., the exhaust port) is not directly cooled with the water, and the distribution of water to each cylinder bank and to each cylinder is not even. Therefore, an imbalance can result in the operation of each cylinder, and such imbalance can adversely impact engine operation.
In addition, and with at least some known marine engines, each cylinder bank includes a blow off valve and a thermostat connected in series in the flow path between the cylinder water jackets and the cylinder head water jackets. At lower speeds, there may not be sufficient pressure to open the blow off valve even though the thermostat may be fully open due to the engine temperature. Such an operating condition can lead to over heating the cylinder heads since only a small volume of water is supplied to the cylinder head.
Further, and since a blow off valve and a thermostat are provided for each cylinder bank, one cylinder bank may operate hot while the other bank is operating within a normal range. For example, if the thermostat of one cylinder bank fails in a closed condition, then very little water will be supplied to the cylinder head for that cylinder bank, and the cylinder head will be hot. The cylinder head for the other cylinder bank may, however, be within the normal temperature range.
The present invention, in one aspect, is a cooling system for a marine engine and includes cylinder cooling jackets, cylinder head cooling jackets, and thermostatic and pressure controls which facilitate safely operating the engine with low water flow rates. In one specific embodiment, the cooling system has multiple failure modes so that even if one of the controls fails, the cooling system still provides sufficient cooling to facilitate avoiding severe damage to engine.
In an exemplary embodiment, the cooling system is employed in a marine engine including a V-type cylinder block with two cylinder banks and a valley between the banks. Each cylinder bank includes a plurality of cylinder bores (e.g., each cylinder bank includes three cylinder bores in a six cylinder engine), and respective exhaust ducts extend from and are in flow communication with each cylinder bore. The exhaust ducts are in flow communication with an engine exhaust housing.
Respective flow paths extend from the valley to a section of each cylinder bore water jacket adjacent each cylinder bore. Specifically, water is provided from the valley to the cylinder bore water jackets near each cylinder exhaust duct extending from each cylinder bore. For example, in a six cylinder engine, respective flow paths extend from the engine valley to each cylinder, i.e., six flow paths. By supplying cooling water from the valley to adjacent each cylinder exhaust duct, a hottest part of the engine is cooled by cooling water from the valley. Providing water from the valley to adjacent each cylinder exhaust duct facilitates uniform cooling of each cylinder and balanced operation of the engine.
Each cylinder bore water jacket includes an outlet at an upper portion of each said cylinder bank. A water flow path extends from each cylinder bore water jacket outlet to a respective cylinder head water jacket. A temperature sensor is thermally coupled to each cylinder head cooling jacket, and provides a signal representative of cylinder head temperature to an electronic control unit (ECU). In the event that the temperature at either cylinder head exceeds a pre-set temperature, ECU limits operation of engine, e.g., to below a pre-set rpm.
Also, variable thermostats are in flow communication with each cylinder bore water jacket, and each thermostat is in flow communication with a water dump passageway, or dump. Each flow path through the respective thermostats is in parallel with a respective cylinder head. Any suitable thermostatic valve which opens above a pre-determined temperature can be employed. The thermostats provide that cooling of the cylinders is thermostatically controlled.
The cylinder head water jackets are in flow communication with a parallel connected blow off valve and thermostat. The blow off valve and thermostat are in flow communication with the water dump. When the blow off valve opens, maximum cooling is provided in that water flows unrestricted from the valley, through the cylinder cooling jackets and the cylinder head cooling jackets, and through the blow off valve to the dump.
The cooling system has multiple failure modes which, in the event of failure of the one of the controls, facilitate avoiding severe damage to engine. For example, in the event one of the thermostats connected between the cylinder and dump fail, the thermostat connected in parallel with the blow-off valve still provides thermostatic control of flow through system. In addition, if all the thermostats fail, the blow-off valve still provides pressure control of flow through system. If the blow-off valve fails, then the thermostats still provide control of flow through system. Further, if the blow off valve fails open, coolant still flows through the engine although the engine may operate cold. While operating the engine cold may not provide optimum efficiency, operating the engine cold facilitates avoiding severe damage to the engine.